Project Summary Persistent pulmonary hypertension of the newborn (PPHN) is a life threatening condition which results from failure of pulmonary vascular resistance to decrease at birth. The affected infants are hypoxemic and have an increased risk of death or long-term impairments for survivors. Recent studies identified 2 key alterations in PPHN lungs: (1) a decrease in mitochondrial biogenesis and oxidative phosphorylation in the pulmonary artery endothelial cells (PAEC) and (2) a decrease in angiogenesis, which contributes to failure of postnatal adaptation of pulmonary circulation. The overall objective of this research project is to identify mechanisms that underlie these 2 key alterations in PPHN. Preliminary studies conducted for this project identified decreased expression of liver kinase B1 (LKB1), a key upstream regulator of the energy sensor, 5?AMP activated protein kinase (AMPK) in PPHN. This alteration contributes to decreased expression of PGC-1?, a transcription cofactor required for mitochondrial biogenesis. Consistent with these changes, mitochondrial biogenesis is decreased in PPHN. In contrast, levels of hypoxia sensor, HIF-1? are increased in PPHN endothelial cells, leading to increase in glycolysis. The PAEC in PPHN show a switch in phenotype to predominantly tip cells from proliferative stalk cells. Whether the altered LKB1-PGC-1? signaling contributes to this phenotype switch is unknown. Studies proposed in this application investigate the hypothesis that decreased LKB1-PGC-1? signaling impairs mitochondrial biogenesis in PAEC and the resulting switch to glycolysis alters the PAEC phenotype specification to impair angiogenesis during a critical window of lung development. The hypothesis will be tested by 2 specific aims: (1) Investigate the role of decreased LKB1-PGC-1? signaling in the impaired mitochondrial biogenesis and increased HIF-1 ? levels in PPHN and (2) Investigate the role of decreased LKB1-PGC-1? signaling in the PAEC phenotype switch and impaired angiogenesis in PPHN. The proposed studies will be done in fetal lambs with PPHN induced by prenatal constriction of ductus arteriosus, a known mechanism of PPHN. Completion of these studies will delineate the mechanism of increased pulmonary vascular resistance in PPHN. These studies will also provide the scientific rationale for testing therapeutic agents to increase LKB1 - PGC-1? signaling and cell permeable metabolic intermediates to restore angiogenesis in PPHN.